1. Field of the Invention
The present invention concerns telemetry systems permitting remote registration of requests for services at a central dispatch point of such services, particularly permitting registration by radio of digitalized service requests at a computerized central dispatch point for taxicab services.
2. Background of the Invention
It is known in the prior art to transmit encoded signals from a multiplicity of remote, transmitting, locations to a central, receiving, location. Such prior art systems are often for transmitting alarms, and for summoning emergency services. Such prior art systems may transfer messages unidirectionally or bidirectionally, including by radio. However, they generally differ from the system of the present invention, amongst other aspects, by failing to transmit message information in digitalized form, by failing to accord for conflicts between multiple messages simultaneously transmitted upon a single communications channel, and by interpreting and processing all messages manually as opposed to interpreting and processing messages by automated, computerized, means.
As an example of the prior art, U.S. Pat. No. 2,022,991 for an ALARM TRANSMITTING SYSTEM discloses an early use of radio in an alarm system. Switches concealed about the protected premises, or even concealed upon the person of an employee, are connected by wires, usually telephone lines, to a central alarm office. Upon the receipt of an alarm resultant from a switch closure at the central alarm office, an associated one telegraph phone reproducing unit is activated so as to broadcast predetermined instructions over a radio transmitter. These predetermined instructions direct a particular police car, assigned to the neighborhood from which the alarm has been received, to proceed to the premises or person upon which the alarm system has been activated. An early attempt showing the use of radio, and an attempt to discriminate between the message and the response thereto, is shown.
U.S. Pat. No. 2,989,621 for FIRE ALARM SYSTEM USING A PLURAL OSCILLATOR RADIO TRANSMITTER to P. M. Barton, et al., shows a fire alarm system using radio rather than wired communication for transmitting alarms from a multiplicity of alarm boxes to a central receiving center. The signals broadcast by the different transmitters within the same alarm system are modulated with different audio tones so that the particular alarm box from which each signal has been sent may be identified. The possibility that more than one alarm may be simultaneously active is encompassed by providing that the number of alarm boxes within each alarm unit system shall be limited to the maximum number of separately and identifiable audio tones, or tone combinations, that can be transmitted within a radio frequency channel. At the preferred operational frequency of 2250 to 2700 kilocycles per second, preferred radio channel band width of 10 kilocycles, and preferred modulation frequency of 400 to 4000 cycles in 100 cycles per second increments, some 37 different audio tones, or 37 alarm boxes, are available per unit system. This modest number, already emplacing a very demanding requirement upon the human ear which must discriminate all combinations of the multiple signals, is evidence of prior art problems with analog (audio frequency) modulation of radio alarm signals, and with the possible interference between such signals.
U.S. Pat. No. 3,256,517 for a REMOTE ALARM SYSTEM WITH SCANNING BY TONES to T. Saltzbert, et al., shows the use of a single transmission channel for a plurality of alarms on a time-shared basis. Particularly, communication via radio link between the remote alarm points and the central stations is bidirectional. The central station transmits interrogations to the remote locations in sequence by use of an addressing code, typically three tones of different frequencies. Each terminal equipment at the remote location responds only to its unique address, and transmits alarm information if and when interrogated. A bidirectional communication system of this nature increases cost. It incurs some latency between the time that an alarm may actually be sensed at a remote station and the later time at which the central station may interrogate the remote station to receive notification of the alarm.
U.S. Pat. No. 3,440,635 for POLICE ALARM to H. B. Hull discloses the use of portable radio transmitters which send coded signals that are received centrally by receivers equipped with direction finding capability. The direction finding equipment is sensitive to transmission of a signal at a particular frequency allocated for this purpose. The allocated carrier frequency may further be modulated with a tone of a particular frequency i.e., it may be encoded, in order to determine the location of the transmitter with increased accuracy. It is contemplated that the number of alarm transmitters, and users, will be small.
U.S. Pat. No. 4,630,035 for ALARM SYSTEM HAVING ALARM TRANSMITTER IDENTIFICATION CODES AND ACOUSTIC RANGING to Stahl, et al., describes an alarm system having a plurality of alarm units each transmitting an identification code. In some systems the alarm transmitters transmit the identification codes to a central control indirectly through one or more transponders. The transponders can also be assigned an address code, and can relay both the alarm transmitter identification code and their own address code to the central control when an alarm condition exists. The alarm units can generate, and the transponders can receive, an audio, as well as a radio, signal in order to aid in positional location of the alarm unit upon the occasion of an alarm.
Prior art telecommunications and telemetry systems for the automated transmission of alarms do not generally address the problem of multiple simultaneous transmissions. This is acceptable because the occurrence of alarms is normally very infrequent. Additionally, the emergency resource which may be provided in response to one or more alarms is usually limited, and it is of little consequence that later, successive, alarms should fail to be recognized if there is no remaining emergency resource to be dispensed in response to such alarms.
A contrary situation exists in a telecommunications, or telemetry, system for the registration of service requests, such as request for transportation services, particularly taxicabs. The number of service requests both per unit time, and at certain peak periods, would be expected to be very large. A number of service requests would normally be expected to be simultaneously, or nearly simultaneously, registered at distributed call boxes each of which is capable of initiating a service request. Finally, a large number of discrete resources, such as taxicabs, are normally available to be applied to the plurality of concurrent service requests. It is therefore useful that no service request should fail to be recognized even though a large system, entertaining many service requests from many distributed call boxes, should use but a single, narrow bandwidth, radio communications channel.
The present invention offers a solution to the telecommunications system problem for reliable registration, communication, and response to multiple asynchronous service requests (particularly transportation service requests, particularly requests for taxicabs). A prior art approach remotely analogous to the solution of the present invention is represented by wired communication channels within and between computers. Particularly, the well-known Ethernet communications channel employing microwave frequency digital communication between discrete points on a coaxial cable accords that a number of interconnected points may each asynchronously attempt to communicate with one or more additional points. In the event that two communications are simultaneously, or nearly simultaneously, initiated, then the receivers at all communicating locations are capable of detecting a collision situation on the communication channel, or coaxial cable. This detection of a collision, or conflict, condition, is based on energy levels. The detection is performed by the transmitting, as well as the receiving, units. In the event of any detection of a conflict, then both transmitting units will cease their attempted communications, and will wait a variable interval of time before asynchronously reinitiating such communications. Since the communications periods typically occupy but a small percentage of the total elapsed time, the stagger-staged communication between transmitting units usually accords that all messages will ultimately flow without conflict on the single communications channel.
It is inappropriate to adapt energy level sensing in order to detect communication conflicts, such as energy level sensing is performed upon an Ethernet communication net, to free space, radio, communication. Particularly, the strength of a radio signal, or signals, may vary in accordance with transmitters' separation(s), transmitters' power(s), and atmospheric conditions. It is unreliable to attempt to determine whether two or more radio transmitters are simultaneously active solely by the sensing of the radio frequency power density.
Alternatively, a full handshake communication system wherein the receipt of all messages is positively acknowledged is also inappropriate. Such a system is more costly resultantly from the use of bidirectional, as opposed to unidirectional, communication links.
The present invention will be seen to permit reliable, fully automated, communication of many independently originated, and asynchronously timed, messages upon a single radio communication channel without incurring either (i) the loss of messages or (ii) a large hardware overhead to ensure message receipt.